A geotechnical composition of soils, strictly speaking, particle size distribution, a water content, and an organic matter content directly affect erosion of soils [Bissonnais, 1996, “Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology,” European Journal of Soil Science, Vol. 47, pages 425-437]. In present days, the erosion of soils is being considered a serious environment problem because the soil erosion has a direct and indirect effect on desertification and climate changes [Gisladottir and Stocking, 2005, “Land degradation control and its global environmental benefits,” Land Degradation & Development, Vol. 16, pages 99-112]. ⅓ of the world's land is currently undergoing the desertification that accompanies the soil erosion, and the desertification is spreading, creating 12 million ha new deserts every year [UNEP (United Nations Environment Programme), 2006, “Deserts & Drylands,” TUNZA the UNEP Magazine for Youth, Vol. 4, No. 1, pages 1-24]. Since the soil erosion causes decrease of productivity of farmlands as well as disturbance of the ecosystem [Gisladottir and Stocking, 2005, “Land degradation control and its global environmental benefits,” Land Degradation & Development, Vol. 16, pages 99-112], development of technologies capable of reducing or suppressing the soil erosion has been urgently demanded.
Conventional methods of suppressing soil erosion have mostly suggested mounting meshes, nets or the like on a soil surface to block external factors (water or wind) causing the erosion [U.S. Pat. No. 3,867,250; U.S. Pat. No. 4,071,400; and U.S. Pat. No. 4,486,120]. However, the externally mounted structures have many limits since they have a time-limited performance and costs much. Accordingly, technologies intended to increase resistance against the erosion by improving soils have been recently suggested [U.S. Pat. No. 4,663,067; U.S. Pat. No. 5,860,770; and U.S. Pat. No. 7,407,993]. However, since the technologies depend on a method of grouting or spraying chemical products, they are irrelevant to the environment-friendly prospect. The soil erosion is primarily attributed to destruction of the ecosystem on a surface layer and an adverse effect of reckless development (slash and burn farming or grazing). Accordingly, the ecological environment should be restored to effectively suppress the soil erosion.
In addition, the geotechnical structure of soils has a direct effect on growth of vegetation. Generally, as the structure of soils is loose, and a water content of soils is high, growth of plants is improved [Passioura, 1991, “Soil structure and plant growth,” Australian Journal of Soil Research, Vol. 28, No. 6, pages 717-728]. Accordingly, for farming, it is important to stir the farmland prior to sowing seeds, or maintain an effective irrigation system. Most of Korean surface soils are granitic residual soils, which are final weathering products of granite, and yellow soil is also a kind of the granitic residual soils [Jin-Yeon Hwang, et. al., 2000, “Composition minerals and chemical components of Korean yellow soil (weathered soils),” Journal of The Mineralogical Society of Korea, Vol. 13, No. 3, pages 146-163]. As yellow soil mainly consisting of halloysite has a dense soil structure, it has been used as a construction material from the past; however, it has been regarded as being inappropriate for vegetation growth.
Thus, there are increasing interests in research for improvement of soils to increase vegetation growth while suppressing the erosion of soils.